docs: def preview(self, obj, request=None):
          """
          Generate the HTML to display for the image.
  
          :param obj: An object with a thumbnail_field defined.
          :return: HTML for image display.
          """
          source = self.get_thumbnail_source(obj)
          if source:
              try:
                  from easy_thumbnails.files import get_thumbnailer
              except ImportError:
                  logger.warning(
                      _(
                          '`easy_thumbnails` is not installed and required for '
                          'icekit.admin_tools.mixins.ThumbnailAdminMixin'
                      )
                  )
                  return ''
              try:
                  thumbnailer = get_thumbnailer(source)
                  thumbnail = thumbnailer.get_thumbnail(self.thumbnail_options)
                  return '<img class="thumbnail" src="{0}" />'.format(
                      thumbnail.url)
              except Exception as ex:
                  logger.warning(
                      _(u'`easy_thumbnails` failed to generate a thumbnail image'
                        u' for {0}'.format(source)))
                  if self.thumbnail_show_exceptions:
                      return 'Thumbnail exception: {0}'.format(ex)
          return ''